Formula Mass & % Comp
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Transcript of Formula Mass & % Comp
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Formula Mass&
Molecular Mass
Formula Mass
Formula mass is the total of all the atomic masses
in a chemical formula.
Formula Mass& Molecular Mass
Every molecular mass
is a formula mass...
Formula Mass& Molecular Mass
but not every formula
mass is a molecular
mass.
Formula Mass& Molecular Mass
Can you explain why?
Formula Mass& Molecular Mass
Are molecules the
only things that have
chemical formulas?
What is the
formula mass
of C2H5OH?
What was the
definition of a
formula mass?
The total of all the atomic masses
in a chemical formula.
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X 2 X 6 X 1
C2H5OH
The total of all the atomic masses
in a chemical formula.
A t o m i c M a s s U n i t s
amu or u
The units offormula mass are:
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C2H5OH
C = 12 X 2 = 24
H = 1 X 6 = 6
O = 16 X 1 = 16
46 u
Formula Mass Calculation
How to do formula masscalculations.
C2H5OH
C = 12 X 2 = 24
H = 1 X 6 = 6
O = 16 X 1 = 16
46 u
Formula Mass Calculation
Write thechemicalsymbolslike this.
C2H5OH
C = 12 X 2 = 24
H = 1 X 6 = 6
O = 16 X 1 = 16
46 u
Formula Mass Calculation
Write theatomicmass ofeach.
C2H5OH
C = 12 X 2 = 24
H = 1 X 6 = 6
O = 16 X 1 = 16
46 u
Formula Mass Calculation
Multiplyby thesubscriptof each.
C2H5OH
C = 12 X 2 = 24
H = 1 X 6 = 6
O = 16 X 1 = 16
46 u
Formula Mass Calculation
Equals
C2H5OH
C = 12 X 2 = 24
H = 1 X 6 = 6
O = 16 X 1 = 16
46 u
Formula Mass Calculation
Circle your answer.Show the units.
C2H5OH
C = 12 X 2 = 24
H = 1 X 6 = 6
O = 16 X 1 = 16
46 u
Formula Mass Calculation
SO4
+2
S = 32 X 1 = 32
O = 16 X 4 = 64
96 u
Formula Mass Calculation
SO4
+2
S = 32 X 1 = 32
O = 16 X 4 = 64
96 u
Formula Mass Calculation
Practice
Calculating
Formula
Mass
What is the
formula mass of
iron (II) sulfate?
FeSO4
FeSO4
Fe
S
O
FeSO4
Fe = 56
S = 32
O = 16
FeSO4
Fe = 56 X 1
S = 32 X 1
O = 16 X 4
FeSO4
Fe = 56 X 1 = 56
S = 32 X 1 = 32
O = 16 X 4 = 64
FeSO4
Fe = 56 X 1 = 56
S = 32 X 1 = 32
O = 16 X 4 = 64
152 u
Formula
Mass
Homework
Assignment
Hydrated Crystals
Crystals that have water
molecules chemically
bonded to
the ions in
the crystal.
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This occurs when a
highly ionic substance
crystallizes from a
water solution.
Although these crystals
are solids, the water
molecules can be
forced out of the crystal
lattice by heating.
CuSO4 5H2O
The formula for "hydrated"
copper (II) sulfate above
indicates there are 5 water
molecules for every 1
copper (II) sulfate.
CuSO4 5H2O
What is the formula mass of
copper (II) sulfate pentahydrate
HINT: treat water as aseparate element in the formula.
CuSO4 5H2O
Cu = 1 X 64 = 64
S = 1 X 32 = 32
O = 4 X 16 = 64
H2O = 5 X 18 = 90250 amu
How much water (in grams) is in 5 gramsof copper (II) sulfate pentahydrate?
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CuSO4 5H2O looks
something like this:
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Anhydrous CuSO4 looks
something like this:
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Percentage Composition
Each element makes up
a % of the substance.
Add one step
to a formula
mass calculation.
Percentage Composition
What is the percentage
composition of C2H5OH?
Percentage Composition
C2H5OH
C = 12 X 2 = 24
H = 1 X 6 = 6
O = 16 X 1 = 16
46 u
Percentage Composition
C2H5OH
C = 12 X 2 = 24
H = 1 X 6 = 6
O = 16 X 1 = 16
46 u
Percentage Composition
Now divide EACH
atomic mass by
the formula mass.
C2H5OH
C = 12 X 2 = 24 / 46 = 52 % C
H = 1 X 6 = 6 / 46 = 13 % H
O = 16 X 1 = 16 / 46 = 35 % O
46 u
Percentage Composition
Practice
Calculating
Percentage
Composition
What is the complete
percentage composition
of sulfuric acid?
H = 1 X 2 = 2
S = 32 X 1 = 32
O = 16 X 4 = 64
H2SO4
98Work as a
formula mass
problem
H = 1 X 2 = 2
S = 32 X 1 = 32
O = 16 X 4 = 64
H2SO4
98
/98 /98
/98
Then divide the
total into each one
H = 1 X 2 = 2
S = 32 X 1 = 32
O = 16 X 4 = 64
H2SO4
98
/98 = 2% H/98 = 33% S
/98 = 65% O
This is the answer
to a % comp problem
Percentage
Composition
Homework
Assignment
Sugar In Bubble Gum